The present invention relates to a receiver using diversity receiving, and in particular, to a diversity receiver including a plurality of antennas.
In radio wave receiving, diversity receiving is used to keep a stable receiving state by preventing such phenomena to cause deterioration of the receiving state as a phenomenon of phasing in which a receiving electric field changes in range and phase with respect to time. Of such diversity receiving, space diversity receiving is a scheme based on an event that the electric field varies depending on radio wave receiving points. Specifically, a plurality of antennas are installed to be spatially separated from each other such that output signals from the antennas are combined with each other or are each obtained through a change-over operation therebetween.
For example, a portable lightweight pager increasingly employs the space diversity receiving (to be simply called xe2x80x9cdiversityxe2x80x9d hereinafter). Namely, the pager includes, to obtain good reception characteristics using the limited space, an extendable and retractable whip antenna for transmission and reception and an integrated antenna dedicatedly used for reception. When receiving radio signals, a change-over operation is conducted according to reception states of the antennas between the antennas to receive an output signal from one of the antennas in a better reception state. FIG. 1 shows an actual example of constitution of a pager using the diversity receiving system. The configuration includes a housing 20 and a whip antenna 18 and an integrated antenna 19 installed in the housing 20.
A diversity receiver adopting the antenna change-over operation usually includes one receiving circuit and at least two antennas. The system determines one of the antennas which operates with highest reception reliability and selects an output signal from the antenna in the better reception state in any situation. Accordingly, the diversity receiver continuously operates in an optimal reception state.
Heretofore, in such a diversity receiver, the antennas other than the antenna selected for the good (best) reception state are not connected to any circuits. Namely, these circuits have a terminating condition specified as xe2x80x9copenxe2x80x9d. Therefore, the antennas not selected as above receive a reception wave of the antenna selected for reception. The antennas are hence driven, and reception waves resultant from the driving of the antennas adversely influence reception characteristics of the selected antenna in some cases.
To possibly avoid occurrence of such a phenomenon, Japanese Patent Laid-Open No. Heisei 10-75192 describes a method in which a transmission line length adjuster circuit is inserted between each antenna and an associated switch to keep a state of each antenna in an optimal state.
However, in the prior art described in Japanese Patent Laid-Open No. Heisei 10-75192, when an antenna on a side at which the adjuster circuit is inserted is used for transmission and reception, send and receive signals are respectively transmitted and received via the adjuster circuit from the antenna. This inevitably leads to loss in the transmission line length adjuster circuit.
Additionally, impedance of a termination point of the antenna in a non-selected state depends on characteristics of the change-over switch. There cannot be obtained a reflection characteristic under an optimal terminating condition. This causes a standing wave and hence noise takes place to lower efficiency of the system depending on cases.
It is therefore an object of the present invention, which has been devised to solve the problems, to provide a highly efficient diversity receiver in which a transmission path length adjuster circuit, namely, a phase adjuster circuit is arranged after a change-over switch relative to or viewed from an antenna to avoid influence of loss in the phase adjuster circuit and a terminator reflection coefficient adjuster circuit is disposed at a terminating point to obtain an optimal reflection characteristic.
In accordance with the present invention, there is provided configurations to solve the problems as follows.
In accordance with one aspect of the present invention, there is provided a diversity receiver including a plurality of antennas, a receiving means for receiving radio waves via said antennas, plurarity of phase adjuster means disposed for each said antenna and connected thereto for adjusting a phase angle of a radio wave received by each said antenna to a value to increase gain of each said antenna to which said phase adjuster means is not connected, and switching means, operative in response to a control signal (S1, S3) indicating a selected antenna having a best reception state to receive an external radio wave, for connecting said selected antenna to said receiving means, for disconnecting said selected antenna from said phase adjuster means and non-selected antennas other than said selected antenna, and for connecting said non-selected antennas to said phase adjuster means associated therewith. The phase adjuster means is connected in a stage subsequent to said switching means viewed from said antennas.
In accordance with one aspect of the present invention, the diversity receiver further includes terminating means disposed for each said antenna and connected thereto for terminating a transmission line and terminating resistor reflection coefficient adjuster means disposed for each said terminating means in a stage after said phase adjuster and before said terminating means for adjusting a reflection coefficient for an input signal fed to said terminating means to a larger value.
In accordance with one aspect of the present invention, the diversity receiver further includes transmitting means for transmitting a signal to said antennas. The switching means connects, in response to a control signal (S2) externally inputted to indicate a transmission state, said transmitting means only to antennas assigned for transmission among said antennas.
In accordance with one aspect of the present invention, said terminating means of the diversity receiver is a resistor.
In accordance with one aspect of the present invention, said terminating resistor reflection adjuster means of the diversity receiver includes a capacitor and a coil.
In accordance with one aspect of the present invention, said terminating resistor reflection adjuster means of the diversity receiver includes a reactance (coil(s)) connected in series between an input thereof and an output thereof and a capacitor connected in parallel between an end of said coil and ground.
In accordance with one aspect of the present invention, said phase adjuster means of the diversity receiver includes capacitors and a reactance (coil(s)).
In accordance with one aspect of the present invention, said phase adjuster means of the diversity receiver includes a strip line or a coaxial line.
In accordance with one aspect of the present invention, each said capacitors of the diversity receiver is a chip capacitor.
In accordance with one aspect of the present invention, the diversity receiver further includes determining and controlling means for detecting a state of a radio wave received by each said antenna, for selecting one of said antenna in a best reception state, and for producing the control signal (S1, S3) indicating said selected antenna or the control signal (S2) indicating a transmission state.
In accordance with one aspect of the present invention, there is provided a transceiver comprising the diversity receiver.
In accordance with one aspect of the present invention, there is provided a portable transceiver comprising the diversity receiver.
In accordance with one aspect of the present invention, there is provided a diversity receiving method comprising the steps of preparing a plurality of antennas, preparing receiving means for receiving radio waves via said antennas, disposing phase adjuster means for each said antenna and connecting said means thereto, adjusting by said phase adjuster means a phase angle of a radio wave received by each of the antennas to a value to increase gain of each of the antennas to which the phase adjuster means is not connected; and connecting, by switching means operative in response to a control signal (S1, S3) indicating a selected antenna having a best reception state to receive an external radio wave, the selected antenna to the receiving means, disconnecting the selected antenna from the phase adjuster means and non-selected antennas other than the selected antenna, and connecting the non-selected antennas to the phase adjuster means associated therewith.
In accordance with one aspect of the present invention, the diversity receiving method further includes the steps of terminating, by terminating means disposed for each of the antennas and connected to a final stage of the antenna, a transmission line; and adjusting, by terminating resistor reflection coefficient adjuster means disposed for each of the terminating means in a stage after the phase adjuster and before the terminating means, a reflection coefficient for an input signal fed to the terminating means to a larger value.